In general, wear adjustment devices are known in different embodiments, e.g. mechanical adjusters of the kind which nowadays ensure a constant release clearance within certain limits in current commercial vehicle disk brakes. Since the adjusters have to maintain a constant release clearance in all driving and braking situations, the requirements on the precision of such adjusters are very high. In particular, this determines the release clearance which must be crossed for pad contact, the pivoting travel of a pivoted lever used for brake application, for example, and thus the maximum braking force that can be applied or the braking force reserve.
In such disk brakes fitted with an adjustment device, the adjustment device is activated in the event of brake actuation and a release clearance that is different from a desired value, e.g. by a feed element of the application device of the disk brake. Thus, if wear occurs on the brake pads and/or the brake disk with a resulting change (increase) in the release clearance, automatic adjustment of the pads is performed by means of the adjustment device, e.g. by an adjusting movement of pressure rams. A release clearance predetermined by the design is reproduced in the form of fixed geometrical quantities in the component elements participating in the adjustment process.
Disk brakes which have an application device actuated by the pivoted lever are known from DE 195 07 308 A1 and DE 10 2008 037 775 B3. In these cases, the application device itself includes a pivoted lever with an eccentrically acting braking shaft, the rotation or sliding axis of which is parallel to the brake disk plane and which acts on a pressure piece that can be moved in the brake caliper. The terms “cross piece” or “bridge” have also been used hitherto instead of “pressure piece”. For the sake of simplicity, therefore, only the phrase “movable element” will be used below. The movable element itself is arranged non-rotatably in the brake caliper. Mounted centrally in the movable element is a pressure spindle device, which has a rotatable adjustment nut provided with a pressure collar and a pressure spindle or actuating spindle screwed into said nut but held non-rotatably. Via these parts, the application force is transmitted to at least one brake pad, which is then pressed against the brake disk.
In the above mentioned disk brakes, the adjustment device is held in a fixed manner in that end region of the adjustment nut provided rotatably and with a pressure collar which is remote from the brake disk. Since the adjustment nut itself is likewise mounted in a fixed manner in the movable element, the adjustment device follows the axial movements of the movable element during application movements. The term “in a fixed manner” refers to the position of the adjustment device both when the brake is unactuated and when the brake is actuated and during the adjustment itself.
The parts belonging to the adjuster can be divided functionally into an input region and an output region, wherein the input region is coupled for conjoint rotation to the pivoted lever. The rotary movement is transmitted via a wrap spring acting as a one-way clutch to the output region, which brings about the rotation of the adjustment nut via a mechanical separating clutch/separating device, which is spring-loaded and thus acts in a load- or torque-dependent manner. The separating clutch/separating device is a friction cone, for example. Since the pressure or actuating spindle screwed into the rotatable adjustment nut is held fixed against relative rotation, it is screwed out in the direction of the brake disk. The adjustment step is ended when, owing to the force stroke, the friction in the adjustment nut mounting or threaded pair rises and exceeds the maximum possible adjustment torque. The torque-dependent clutch then slips, thereby preventing elastic brake deformations during the force stroke from affecting the adjustment travel.
In the brakes described above, those parts which belong to the adjuster are connected in series when viewed in an axial direction and are connected in a fixed manner to the movable element. This requires an appropriate installation length in the axial direction. Since the brake application parts, i.e. the adjustment nut and the pressure spindle, furthermore take up a corresponding installation space, it is not possible to increase the size of the parts in order to achieve higher application forces owing to the predetermined caliper shape. Moreover, the adjusting parts which form the spring-loaded mechanical separating device in all the adjustment devices are subject to relative wear in the contact regions, and this affects the accuracy of adjustment.
DE 40 34 165 A1 discloses a disk brake having a movable element referred to as a cross piece. The movable element is provided with a threaded bore, into which is screwed an actuating spindle connected operatively to an adjustment device (rotary drive) for setting the release clearance. In this brake, the totality of the adjustment device serving as a rotary drive is designed as a coherent subassembly of elongate or tubular design in the axial direction. This device is inserted into the interior of the caliper through a caliper opening facing away from the brake disk and is secured in a fixed manner there on the caliper end, with the result that it extends into an opening in the actuating spindle. The rotary drive therefore lies concentrically within the hollow rotary spindle. In this case, the rotary drive or the output part thereof is coupled in a non-rotatable but axially movable manner to the actuating spindle via axial profiles. In this way, the rotary movements of the adjuster are transmitted to the actuating spindle. With increasing wear adjustment, the actuating spindle is screwed out of the movable element in the direction of the brake pad or brake disk and is thus also moved axially relative to the fixed-location adjuster. Friction clutches or ratchet mechanisms, which are each spring-loaded and act mechanically, are used as the torque-dependent separating device within the adjuster subassembly.
Since the adjuster in the brake according to DE 40 34 165 A1 is secured in a fixed manner on the brake caliper and the movable element referred to as a cross piece is moved with the adjusting spindle in each actuation, opposed relative movements take place in the contact regions between the adjuster or the output part thereof and the adjusting spindle, and rotary movements are furthermore superimposed on these movements during an adjustment step. Since the application device, on the one hand, and the adjustment device, on the other, are separate subassemblies here, this requires a corresponding assembly effort. Moreover, the opposed relative movements can affect the accuracy of adjustment.
The brake according to German Utility Module 92 06 052 includes an application device having a pivoted lever and a pressure spindle device, which is not mounted in an additional movable element but is mounted directly in the brake caliper. The adjustment device, in turn, is held in a fixed manner on the brake caliper and rests as a separate subassembly on an axis parallel to the rotation axis of the pressure spindle device. The rotary movements are transmitted by the adjuster to the pressure spindle device via a gear mechanism.
A similar disk brake to that in German Utility Model 92 06 052 is shown in EP 1 852 627 A2. Admittedly, it is designed as a single-spindle brake. On the other hand, however, a parallel offset is provided between the adjuster and the pressure spindle device, with a gear mechanism situated in between.
Both the brake according to German Utility Model 92 06 052 and that according to EP 1 852 627 A2 are provided with mechanically acting separating devices (friction clutch), which are controlled by spring force and are intended to prevent excessive adjustment in the force stroke.
The disk brake according to DE 10 2005 003 223 A1 is a double-spindle brake of similar basic construction to the initially mentioned brakes according to DE 195 07 308 A1 and DE 10 2008 037 775 B3. Once again, a pressure spindle device having an adjustment nut and an actuating spindle is namely mounted in a movable element. The adjustment device is attached in a fixed manner to the movable element, on the one hand, and—as in DE 40 34 165 A1 too, for example—attached in a fixed manner to the brake caliper end, on the other hand. Since, here too, opposed relative movements take place—even within the adjustment device—the first and second regions of the adjuster are coupled by means of an axial connecting clutch (dog clutch). This adjustment device too has a mechanically acting separating device (slipping clutch) in order to avoid excessive adjustments.
DE 20 2006 021 050 U1 shows an adjustment device, which is held in a fixed manner on the brake caliper, mounted between two pressure rams and situated in the force flow of brake application, and a mechanical separating device acting load- or torque-dependently in the form of an axially acting ball clutch in order to avoid excessive adjustment.
DE 43 07 018 A1 shows a disk brake having an adjustment device which is held in a fixed manner on the brake caliper in all operating states and the output part of which extends longitudinally in the actuating spindle. It is connected operatively or coupled to the actuating spindle by means of a profiled disk in a manner which prevents relative rotation but allows axial movement. As a rotary drive for adjustment via a one-way clutch use is made of a torsion spring leg coupled directly to the pivoted lever, wherein the torsion spring acts as an overload safeguard and as an energy storage device in order to adjust the lining wear which takes place during the braking process, possibly also during the brake release stroke. Apart from the disadvantageous opposed relative movements during the application and adjustment process in the contact regions between the application device and the adjuster itself, the embodiment and mounting of the adjuster both with respect to the pivoted lever and the brake caliper and also mounting with respect to the adjusted parts relative to one another owing to frictional effects are fault-prone, in particular. Accuracy of adjustment could thus be impaired. Since, furthermore, the brake application and adjustment parts are arranged in series in the brake caliper—when viewed axially—the resulting overall caliper lengths do not meet the requirements in respect of the restricted installation conditions in the commercial vehicle. Moreover, the assembly effort does not meet all the requirements for automation.